For something that’s not especially provocative, Sheila Callaghan’s new play at Rattlestick Playwrights Theater sure is dodgy to talk about. After all, you have to be careful about the company you keep if you’re going to try explaining why things like dyslexia, murder, and humiliating sexual assault can indeed be big-time laughing matters. But silver-plated comedy they are in That Pretty Pretty; or, The Rape Play, one of the funniest theatrical takes on categorically unfunny subjects since Martin McDonagh made a fall-down riot of domestic terrorism in The Lieutenant of Inishmore.

Alas, Callaghan does not possess McDonagh’s peerless plotting ability, his nimble way of approaching an unexpected joke from five directions simultaneously, or his on-the-sleeve social conscience. That makes her play, which has been decisively but wobbily directed by Kip Fagan, more mirth-inspiring than insightful. But even if Callaghan works too hard to drive home her points - and if they’re usually blunted when she does - you can’t help but be grateful for the zany trip to the underworld she makes possible.

Your companions for the journey are Agnes and Valerie (Lisa Joyce and Danielle Slavick), two “female Dukes of Hazzard” sisters traversing America seducing and murdering radical pro-life advocates, then blogging about their conquests; Owen and Rodney (Greg Keller and Joseph Gomez), two men who, depending on the circumstances, are either the women’s victims, their stalkers, or their Pygmalions; and Jane Fonda (Annie McNamara). Yes, that Jane Fonda: she of the Workout, the Vietnam War infamy, 33 Variations (currently on Broadway), and inspiration - of different kinds - to women and men the country over.

Each scene suggests a new relationship for the quintet: a hotel smackdown revolving differently around each gender group, a mostly wordless comedy of manners, a Hollywood pitch plot à la Speed the Plow. Up to the last scene, you’re kept merrily in the dark about what’s happening and why; even after the finale offers its definitive, if still ambiguous, interpretation, you still might not be sure. But because the dialogue is engagingly jagged, the pacing sure, and most of the performances in the proper comic key (McNamara, who’s not at all believable as Jane Fonda, has it the toughest), that’s barely a problem.

But the excess does begin to wear after a while. Roughly a quarter of the 105-minute running time is devoted to setting up and paying off two gags of legitimate but limited humor value. In fairness, one has what one of the most eye-pokingly bizarre punch lines in theatre history (“I want to make a movie my mom could be proud of!” - you have to be there), and the other is a full-scale genre parody along the lines of the first 10 minutes of last year’s movie war-drama comedy Tropic Thunder. Each has an unimpeachable reason for being included, but is inflated for purposes only a visionary playwright could justify.

Callaghan’s goal, however, is obtusely stated and unconvincingly argued. Her juxtaposition of rabid activism of any sort with female exploitation is intriguing but shakily defended. She obviously has something important to say about how women treat themselves and are treated by others on the Internet, in films, and in the bedroom. But her numerous detours and pit stops, paired with Fagin’s trouble maintaining the breakneck pace necessary to keep you forever off your guard, require you to spend most of the time struggling to keep your destination in view. By the time the girls start Jell-O wrestling onstage around the two-thirds mark, you’re ready for it to be over. (Okay, maybe just after the Jell-O wrestling.)

The playwright’s clearest statement seems to be about entertainment’s tendency toward overanalysis, especially as an excuse for perpetuating hatred and stereotypes under the guise of fairness and equality. This topic is always timely, and the more That Pretty Pretty veers in this direction, the steadier - if more serious - it feels. But then a character states he’s “merely giving voice to the unspoken” or asks “Why is truth so controversial?” and brings down the house (for reasons too tangled to explain here), and you find yourself wondering to what degree everything is present only for the sake of cheap humor.

Dwell on such issues for too long, though, and you’ll miss one of the raunchiest and most ridiculous joyrides of the winter theatre season. Since most of us need all the levity we can get these days, the best way to absorb what the play is emanating is to close your mind, open your ears, and gird your gut - the messages won’t start until the laughter stops. That Pretty Pretty would be even better if you didn’t have to wait even longer for those messages to make sense.